wm8400 Wolfson Microelectronics plc, wm8400 Datasheet - Page 56

• Manufacturer Part Number: wm8400
• Description: Wolfson Audioplustm Hi-fi Audio Codec And Power Management Unit For Mobile Multimedia
• Manufacturer: Wolfson Microelectronics plc

WM8400
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Up to four microphones can be connected to the WM8400, either in single-ended or pseudo-
differential mode. A low noise microphone bias is fully integrated to reduce the need for external
components.
In single-ended microphone input configuration, the microphone signal is connected to the inverting
input of the PGA (LIN1, LIN3, RIN1 or RIN3). The non-inverting input of the PGAs should be
internally connected to VMID in this configuration. This is enabled via the Input PGA configuration
register settings. In this configuration, LIN2, LIN4, RIN2 or RIN4 may be free to be used as line
inputs or ADC bypass inputs.
In pseudo-differential microphone input configuration, the non-inverted microphone signal is
connected to the non-inverting input of the PGA (LIN2, LIN4, RIN2 or RIN4) and the inverted (or
noisy ground) signal is connected to the inverting input (LIN1, LIN3, RIN1 or RIN3).
Any PGA input pin that is used in either microphone configuration should not be enabled as a line
input path at the same time.
The gain of the input PGAs is controlled via register settings. Note that the input impedance of LIN1,
LIN3, RIN1 and RIN3 changes with the input PGA gain setting, as described under “Electrical
Characteristics”. (Note this does not apply to input paths which bypass the input PGA.) The input
impedance of LIN2, LIN4, RIN2 and RIN4 does not change with input PGA gain. The inverting and
non-inverting inputs are therefore not matched and the differential configuration is not fully
differential.
MICROPHONE INPUTS
Figure 20 Single-Ended Microphone Input
Figure 21 Differential Microphone Input
PP, April 2009, Rev 3.0
Pre-Production
56